1. Field of the Invention
This invention relates to a specialized scanner and method of inspecting the integrity of spot and seam welds and more particularly it relates to an ultrasonic, nondestructive method of inspecting spot and seam welds.
2. Description of the Prior Art
Heretofore, the inspection of spot and seam welds has been performed using visual, radiographic and ultrasonic methods; as described in the Nondestructive Testing Handbook (Metals Handbook, 9th Edition, Volume 17, “Nondestructive Evaluation and Quality Control”, ASM International, Metals Park, Ohio, September, 1989, pg. 335) and the Metals Handbook (Nondestructive Testing Handbook, 2nd Edition, Volume 7. “Ultrasonic Testing”, American Society for Nondestructive Testing, Columbus, Ohio, 1991, pgs. 10–12 and pgs. 557–566). The visual and radiographic methods reveal little or nothing concerning the fusion of these welds. The prior art ultrasonic method referred to in the literature as a pulse-echo method however is generally referred to as a ring down technique throughout the industry (Nondestructive Inspection of Spot Welds, Overview of Symposium held at Center for Nondestructive Evaluation Nov. 6, 1997). It makes use of the reflected amplitude and the envelope formed in time by many multiple reflections. Basically an envelope of these reflections are used to indicate if the weld is fused or not. Destructive sampling techniques of welds have also been in use. This has been done by either separating the sheets with a chisel or with a tensile pull technique. Another destructive technique in common use cuts through the weldment, polishes and enhances the weldment so that the dimensions of the fused part of the weld can be measured optically. In this prior art, (Recommended Practices for Test Methods for Evaluating the Resistance Spot Welding Behavior of Automotive Sheet Steel Materials, SAE publication ANSI/AWS/SAE/ D8.9-97; Specification for Resistance Welding of Carbon and Low-Alloy Steels, American Welding Society, AWS C1.4M/C1, 4:1999), the part is destroyed and the dimensions of the weld are used to infer the weld quality.
Although there are many ultrasonic transducers and scanners in the prior art none has adapted to the features needed to measure the unique parameters and topology encountered in spot welds. The prior art has used immersion scanners for making B-scan and C-scan images that are convenient for making the measurements required. This process requires the part be placed in a tank of water having sufficient volume to immerse the spot weld being inspected, orienting the part to the transducer and scanner axis and drying the part afterwards. The immersion tank must fit the largest part and, as a result is usually too large to be made portable. The water in the tank requires conditioning and adds to the size of the system. A skilled operator is required to use such equipment to make proper images.
It would be advantageous to have a technique and system that includes the capability to accurately measure dimensions of fusion in the weldment and to determine the presence of weld defects. Using the dimensions of the fused sections as a quality indicator would make the ultrasonic process highly reliable and accurate and save on industrial injury which sometimes occurs during the expensive destructive quality tests of welds. Additionally, a compact, lightweight scanner that is better adapted to the scanning needs of spot weld inspection in a factory environment is needed, one that can make all the measurements, in the manufacturing environment, and require lessor skills and training. The present invention provides such a technique and system, as well as a compact, lightweight scanner design.